Theft control system



Oct. 22, 1968 E. M. LURIE THEFT CONTROL SYSTEM Filed Aug. 20, 1965 United States Patent() 3,407,400 THEFT CONTRGL SYSTEM Eli M. Lurie, 9349 Abbott Ave., Surfside, Fla. 33154 Filed Aug. 20, 1965, Ser. No. 481,234 22 Claims. (Cl. 340-280) ABSTRACT F THE DISCLOSURE A- theft control system for a plurality of appliances is constructed of -a bridge circuit in which there is a common out-put terminal and a plurality of additional output terminals each individual to one of the `appliances being protected. Under normal conditions the application of a potential difference `across the input terminals of the bridge result in zero potential difference appearing between each of the additional output terminals and the common input terminal. Each of the appliances is provided with an impedance elementy forming part of the bridge circuit and connected to one of the additional output terminals in such a manner that when the energizing cable for the appliance is disconnected or severed, the impedance element located at this appliance is disconnected from the bridge, thereby unbalancing it `and causing a potential difference to exist across the output terminals. The primary of a step-down transformer is connected in series wit-h a neon indicator lamp with an individual lamp being provided for each appliance being protected and each of these lamps being connected in series with the transformer primary. These lamps are located at a central control panel together with an audible yalarm connected to the transformer secondary.

n This invention relates to alarm systems in general and more particularly relates to a system of this type for detecting attempted theft of an appliance with the alarm being at a control panel remote from the location of the appliance in question.

Today it is very common for each room of a hotel or motel to be provided with a television receiver suitable for home use. In the absence of a suitable theft control system it is a simple matter for a transient to steal such television receiver and the theft may not be detected until many hours or many days later.

Motels and hotels often have many hundreds o-f television receivers each in a different room with some being a considerable distance from the front desk. The prior art has lattempted `to provide suitable theft detection systems for this purpose but these systems have proven to be either too costly or their performance has 'been less than satisfactory.

Accordingly, a primary object of the instant invention is to provide a novel theft control system for a plurality of appliances, with the system being more economical and/or more reliable than prior :art systems for accomplishing similar purposes.

Another object is to provide a theft control system of this type which requires only a single insulated lead for connecting the appliance in question to the theft control panel at the front desk.

Sitll another object is to provide a theft control system of this type utilizing a plurality of bridge circuits lall of which have a common leg.

A further object is to provide a 4theft control syste-m of this type in which a plurality of bridge circuits `are provided and a theft is indicated by unbalance in a bridge circuit with this unbalance being detected by a common transformer primary connected in series with a plurality of neon lamps, one such lamp being provided for each of the appliances being protected.

3,407,400 Patented Oct. 22, 1968 ICC A still further object is to provide a theft control system for television receivers constructed such that an alarm is actuated Whenever the receiver line cord or the master antenna lead is -unplugged or severed.

These as well as other objects of the inst-ant invention will become readily apparent after reading the following description of the accompanying drawings in which:

FIGURE l is a front elevation of a control panel for a theft control system constructed in :accordance with the teachings of the instant invention.

FIGURE 2 is an electrical schematic of a theft control system constructed in accordance with the teachings of the instant invention. i

FIGURE 3 is an electrical schematic Iof a portion of FIGURE 2 illustrating the bridge circuit for an individual appliance.

Now referring to 'the figures. The theft control system of the instant invention includes control panel 10 (FIG- URE l) typically at the front desk or other suitable location of a motel. Panel face 11 is provided with an individual neon indicator lamp 101g, 102a, 10311, etc. for each room `of the establishment as well as a single pole switch 101b, 102b, 103b, etc. -connected in series with the indicator lamps 101a, 102a, 103a, etc., respectively, as shown in the electrical schematic of FIGURE 2. Also located on panel face 11 are single pole switch 12, reset switch 13 and theft indicating means lamp 14 each of which will hereinafter be described in connection with the description of FIGURE 2. Line cord 15 is provided for connecting control panel 10 to a llO volt 60 cycle source Vof energizing power and -multi-conductor cable 16 is provided for connecting control panel 10 to ythe appliances being protected.

Television receiver 17 (FIGURE 2) located in room 101 is energized through the conductors of line cord 18 connected to prongs 21, 22. When plug 20 is inserted into wall `mounted receptacle 19 with prongs 21, 22 engage receptacle contacts 23, 24, respectively, connected to opposite terminals of a 110 volt 60 cycle source. Receiver 17 is connected to a master antenna system through coaxial cable 25 having grounded sheath 26. Sheath 26 is connected to Iantenna cable plug 27 which when inserted into antenna receptacle 28 at the 4back of receiver 17 grounds receptacle shell 29.

The portion of the theft control system specific to television receiver 17 includes the bridge circuit best seen in FIGURE 3. Terminals A and B are the input terminals for energizing the circuit while terminals C and D are the output terminals thereof. Resistor 31, connected between terminals A and C, and resistor 32, connected between terminals B and C, form one leg of the bridge while resistor 33-1, connected between terminals A and D, and resistor 34-1, connected between terminals B and D, form the other leg of the bridge. Resistors 31, 32, 33-1 and -34-1 are so proportioned that normally zero potential exists between output terminal C, D.

A series circuit consisting of neon indicator lamp 101a, switch 101b and the primary winding 36 of step down transformer 35 (FIGURE 2) extends from terminal D to terminal C. Input terminal B is connected to the ground conductor running throughout the `building with one end of resistor 32 being xedly connected to this ground Within panel 10. Resistor 34-1 is located within television receiver 17 being connected at one end to receptacle shell 29 and at the other end to the conductor of line cord 18 connected to plug prong 38. When plug 20 is inserted into receptacle 19, prong 38 engages receptacle contact 39 connected through insulation covered conductor 40 extending to output terminal D located at control panel 10. Input terminals A, B are connected to opposite ends of the secondary winding 44 of transformer 3 42 whose primary winding 43 is energized through line cord 15.

Secondary winding 37 of step down transformer 35 is connected to control ring of SCR 45. More particularly, one end of winding 37 is connected to base electrode 46 while the other end of Winding 37 is connected to emitter electrode 47 as well as to the negative terminal of DC source 49 located at or near control panel 10. Collector electrode 48 is connected through normally closed reset switch 13, switch 12 and winding 51 of the indicator means buzzer to the positive terminal of source 49. indicating means lamp 14 is connected across buzzer winding 51 and switch 12.

Under normal conditions, that is, when television receiver 17 is properly connected to master antenna cable 25 and receptacle 19, the bridge circuit of FIGURE 3 is balanced. Normally, SCR 45 is non-conducting. Under these normal conditions zero potential exists across output terminal C, D. Should the ground connection to resistor 34-1 be severed as by disconnecting antenna lead 25 from receptacle 28 or should the other end of resistor 34-1 be disconnected from output terminal D, as by severing line cord 18 or removing plug 2f) from receptacle 19, the bridge circuit of FIGURE 3 will` be unbalanced. Current will now flow between output terminals C and D with this current being of sufficient magnitude to illuminate neon indicator lamp lilla. This current also flows through primary winding 36 of step down transformer 35 inducing a voltage in secondary winding 37 of sutiicient magnitude to trigger SCR 45 into conduction.

Once SCR 45 begins to conduct it will remain conducting even though the control signal is discontinued. Conduction through SCR 45 actuates the alarm buzzer when switch 12 is closed and also illuminates indicating means lamp 14. By opening switch 12 the indicating means buzzer will be deactuated but indicator means lamp 14 will continue to be energized until SCR 45 stops conduction. The latter is accomplished by momentarily disconnecting the emitter collector circuit 47, 48 from source 49 by opening reset switch 13.

Each of the other television receivers being protected against theft are provided with resistors corresponding to resistors 33-1 and 34-1 as well as individual neon indicators and switches corresponding to indicator h: and switch 101b. Thus, the television set in room 102 has mounted therein resistor 34-2. At panel 10 resistor 33-2, connected from terminal A to indicator 102er, is provided for the television receiver in room 162. Indicator 102a is connected through switch 102b to line E connected to the juncture between switch 10211 and primary winding 36 of transformer 35.

Since the current required to illuminate the neon indicators 101:1, 102:1, 103e, etc. is relatively small many hundreds of television receivers may be connected to a bridge circuit means having a common leg consisting of resistors 31, 32 and a common detecting means transformer 35. Even if an attempt is made to steal all of the television sets at about the same time indications of each individual attempted theft will produce an individual signal at control panel l0. Switches 101b, 102b, 103b, etc. are provided in the event a television receiver must be removed for servicing.

Thus, this invention provides a novel theft control systern for a plurality of appliances. This control system is so constructed that only a single insulated conductor is required for connecting the appliance in question to a remote supervisory control panel with the common ground of the building providing another electrical conductor. The system is so constructed that a potential thief would not be able to defeat the system. This system is more reliable and lower in cost than prior art devices intended to perform the same functions.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art.

Therefore, this invention is to be limited, not by the speciiic disclosure herein, but only by the appending claims. The embodiments of the invention in which lan exclusive privilege or property is claimed are defined as follows.

1. An alarm system for preventing theft of an appliance; said system including a bridge circuit having input terminals through which said bridge circuit is energized; and a first and a second leg each extending between said input terminals; a first and a second impedance element serially connected in said first leg; a third and a fourth impedance element serially connected in said second leg; output terminals, one in said first leg between said first and second impedance elements and the other in said sccond leg between said third and said fourth impedance elements; a control Apanel having said first and second irnedance elements located thereat; said fourth impedance element positioned remote from said panel and mounted to an appliance being protected; said impedance elements proportioned so that with said bridge circuit energized by applying a difference in potential across said input terminals substantially zero potential difference normally exists between said output terminals; detecting means connected between said output terminals for detecting the existence of a potential difference between said output terminals; indicating means coupled to said detecting means and energized in response to the occurrence of a potential difference between said output terminal; a transformer having a primary and a secondary; said detecting means including said primary; said secondary coupling said indicating means to said detecting means.

2. An alarm system as set forth in claim 1 in which the detecting means also includes an indicator located at said panel.

3. An alarm system as set forth in claim 2 in which the indicator is connected in series with the primary.

4. An alarm system as set forth in claim 3 in which the indicator is comprised of a neon lamp.

5. An alarm system as set forth in claim 3 in which voltage is stepped down between said primary and said secondary.

6. An alarm system as set forth in claim 5 in which the fourth impedance element is mounted within an appliance being protected.

7. An alarm system as set forth in claim 4 in which the neon lamp, the third impedance element and the transformer are mounted at said control.

8. An alarm system as set forth in claim 1 in which a single electrical insulated lead wire connects said control panel to an appliance being protected.

9. An alarm system for preventing theft of an appliance; said system including a bridge circuit having input terminals through which said bridge circuit is energized; and a first and a second leg each extending between said input terminals; a first and a second impedance element serially connected in said first leg; a third and a fourth impedance element serially connected in said second leg; output terminals, one in said first leg between said first and second impedance elements and the other in said second leg between said third and said fourth impedance elements; a control panel having said rst and second impedance elements located thereat; said fourth impedance element positioned remote from said panel and mounted to an appliance being protected; said impedance elements proportioned so that with said bridge circuit energized by applying a difference in potential across said input terminals substantially zero potential difference normally exists between said output terminals; detecting means connected between said output terminals for detecting the existence of a potential difference between said output terminals; said detecting means including an indicator located at said panel; an impedance transforming means including a relatively high impedance input portion and a relatively low impedance output portion; said detecting means including said input portion; said output portion coupling s aid indiatingmeans to said detecting means.

10. An alarm system for preventing appliance thefts; said system including a bridge circuit means having input terminals through which said bridge circuit is energized; a first leg and a plurality of second legs each associated with and connected to an individual appliance being protected; all of said legs connected inparallel and extending between said input terminals; a first and a second impedance element serially connected in said first leg; each of said second legs including an individual third and an individual fourth impedance element connected in series; a first output terminal in said first leg between said first and second elements; for each of said second legs a second output terminal between said third and said fourth elements of that second leg; a control panel having said first and second elements located thereat; each of said fourth elements positioned remote from said panel and mounted to an individual appliance associated with the second leg having the fourth element in question; said elements proportioned so that with said bridge circuit energized by applying a difference in potential across said input terminals substantially zero potential difference normally exists between said first output terminal and each of said second output terminals; detecting means for detecting the existence of a potential difference between said first output terminal and any of said second output terminals; said detecting means including an indicator individual to each of said second legs and connected to the second output terminal thereof; an impedance transforming means including a relatively high impedance input portion and a relatively low impedance 4output portion; said detecting means including said input portion; said output portion coupling said indicating means to said detecting means.

11. An alarm system for preventing appliance thefts; said system including a bridge circuit means having input terminals through which said bridge circuit is energized; a first leg and a plurality of second legs each associated with and connected to an individual appliance being protected; all of said legs connected in parallel and extending between said input terminals; a first and a second impedance element serially connected in said first leg; each of said second legs including an individual third and an individual fourth impedance element connected in series; a first output terminal in said first leg between said first and second elements; for each of said second legs a second output terminal between said third and said fourth elements of that second leg; a control panel having said first and second elements located thereat; each of said fourth elements mounted to an individual appliance associated with the second leg having the fourth element in question; said elements proportioned so that with said bridge circuit energized by applying a difference in potential across said inputterminals substantially zero potential difference normally exists between said first output terminal and each of said second output terminals; means for detecting the existence of a potential difference between said first output terminal and any of said second output terminals; said detecting means including an impedance means individual to each of said second legs and connected to the second output terminal thereof; indicating means coupled to said detecting means and energized responsive to the occurrence of a potential difference between said first output terminal and any of said second output terminals; a transformer having a primary and a secondary; said detecting means also including said primary; said secondary coupling said indicating means to said detecting means; said primary connected in series with each of said impedance means.

12. An alarm system as set forth in claim 11 in which voltage is stepped down between said primary and said secondary.

13. An alarm system as set forth in claim 12 in which each of said impedancemeans is comprised of an indicator located at said panel.

14. An alarm system as set forth in claim 13 in which each of said indicators is comprised` of a neon lamp.

15. An alarm system as set forth in claim 14 in which there is a reset means at said panel for said indicating means; said indicating means once energized remaining energized until the potential at all of said second output terminals is restored to that at said first output terminal and said reset means is operated.

16. An alarm system as set forth in claim 14 in `which the transformer and each of said third elements are located at the control panel.

17. An alarm system as set forth in claim 14 in which there is an individual single insulated lead wire connecting said control panel to each appliance being protected.

18. An alarm system as set forth in claim 14 in which each of said fourth elements is mounted within an appliance being protected.

19. An alarm system as set forth in claim 14 in which there is an individual multi-conductor cable, having conductors through which power is applied, for each appliance being protected; for each of said cables another conductor thereof connecting one end of the fourth element, mounted to an appliance energized through said cable, to a lead wire connecting this appliance to the control panel.

20. An alarm system as set forth in claim 19 in which one of said input terminals is grounded at said control panel and the other end of each of said fourth elements are grounded at those respective appliances to which the fourth elements are mounted by means separate from the conductors of the cables for energizing such appliances.

21. An alarm system for preventing theft of an appliance; -said system including a bridge circuit having input terminals through which said bridge circuit is energized; and a first and a second leg each extending between said input terminals; a first and a second impedance element serially connected in said first leg; a third and a fourth impedance element serially connected in said second leg; output terminals, one in said first leg between said first and second impedance elements and the other in said s-econd leg between said third and said fourth impedance elements; a control panel having said first and second impedance elements located thereat; said fourth impedance element positioned remote from said panel and mounted to an appliance being protected; said impedance elements proportioned so that with said bridge circuit energized by applying a difference in potential across said input terminals substantially zero potential difference normally exists between said output terminals; detecting means connected between said output terminals for detecting the existence of a potential difference between said output terminals; indicating means coupled to said detecting means and energized in response to the occurrence of a potential difference between said output terminals; an impedance transforming means including a relatively high impedance input portion and a relatively low impedance output portion; said detecting means including said input portion; said output portion coupling said indicating means to said detecting means.

22. An alarm system for preventing appliance thefts; said system including a bridge circuit means having input terminals through which said bridge circuit is energized; a first leg and a plurality of second legs each associated with and connected to an individual appliance being protected; all of said legs connected in parallel and extending between said input terminals; a first and a second impedance element serially connected in said first leg; each of said second legs including an individual third and an individual fourth impedance element connected in series; a first output terminal in said first leg between said first and second elements; for each of said second legs a second output terminal between said third and said fourth elements of that second leg; a control panel having said first and second elements located thereat; each of said fourth elements mounted to an individual appliance associated with the second leg having the fourth element in question; said elements proportioned so that with said bridge circuit energized by applying a difference in potential `across Said input terminals substantially zero potential dilerence normally exists between said first output terminal and each of said second output terminals; means for detecting the existence of a potential difference between said rst output terminal and any of said second output terminals; said detecting means including an impedance means individual to each of said second legs and connected to the second output terminal thereof; indicating means coupled to said detecting means and energized responsive to the occurrence of a potential difference between said first output terminal and any of said second output terminals; an impedance transforming means including a relatively high impedance input portionand a relatively low impedance output portion; said detecting means including said input portion; said output portion coupling said indicating means to said detecting means.

References Cited Downer 340-285 X JOHN w. CALDWELL, Primm Examfn'erf D. L. TRAFTON, Assistant Examiner. n v 

